1. Field of the Invention
This invention is concerned with a device for joining by calendering at least one sheet of glass and at least one film of plastic material. The device is composed of a series of pressure rollers mounted side-by-side in a flexible manner and cooperating with the pressure rollers, it being understood that the pressure rollers and the counterpressure rollers are each mounted at the extremity of a piston rod, the other extremity of which bears a pressure piston actuated by pneumatic pressure and moving in a pneumatic casing.
2. Discussion of the Related Art
Calendering devices of this type are used particularly in the manufacture of automobile windows of laminated glass which are cylindrically or spherically curved, and serving to calender thicknesses of glass and plastic material to be joined or laminated in such a manner that the air occluded between these layers is expelled as far as possible and that a temporary reciprocal joining of the various layers is obtained. Thanks to their flexible mounting, the position of the individual pressure rollers adapts itself to the particular shape of the laminated window. The final joining together of these layers is effected, after a preliminary pressing operation, in the course of an autoclave process involving high temperature and high pressure.
In the case of a known calendering device of the aforementioned type (U.S. Pat. No. 2,983,635), the pressure required is produced by pneumatic jacks in which the pressure piston is in direct contact with the inside wall of the cylinder of the jack, and in this manner provides tightness for the cylinder chamber into which the pressure is introduced. In the case of this known arrangement, the mobility of the pressure rollers leaves much to be desired, due to the inevitably produced friction, and consequently the risk of breaking is increased during the calendering of the laminated window. Because of the friction of the pressure roller in the cylinder of the jack, it becomes necessary, during a change of the shape of the glass sheet, to first use a relatively great force, to wit, the so-called "tearing" force (difference of the frictional force between the static friction and the sliding friction), in such a manner that the piston overcomes the static friction at the level of the cylinder wall. The tearing force required for the individual pressure rollers may, in this case, assume values exceeding the bending stress permissible for a glass sheet, so that it results in breaking of the glass sheet.